Issue:
A Ford passenger sedan was struck from behind by a second sedan.  The day after the collision, the driver of the Ford sedan claimed that she braced hard for impact and that her vehicle was hit from behind at approximately 40 mph.  Could the rear-end collision have injured her temporomandibular joint?

TMJ: The joint where the lower jaw (mandible) joins the temporal bone of the skull immediately in front of both ears. A small disc of cartilage separates the bones.

Results:
A reconstruction of the accident demonstrated that the change in velocity of the Ford sedan at impact was less than 2.5 mph with a maximum acceleration of 1.14 G.  Based on the extremely low level of loading, the lack of blunt trauma to the driver, and a careful review of the literature on low-speed rear-impact collisions, Northstar Biokinetics determined that it was improbable that the driver of the Ford sedan would have sustained even a mild soft tissue injury.  Human-subject studies have revealed no jaw motion during rear-end collisions at impact speeds of less than 10 mph; in fact, normal chewing has a greater potential to produce injure to the TMJ.  Northstar Biokinetics concluded, therefore, that there was no causal link between the driver’s temporomandibular joint dysfunction and the rear-end collision.